am: do not account totalSwapPss as used RAM

Process PSS swapped is accounted as part of total process Pss to
get similar Pss values whether the device is using ZRAM of not.
But SwapPss is compressed in RAM so should not be accounted as
direct RAM contributor but though getZramTotalSizeKb already
taking into account.

Change-Id: I944850fb2a2b3a7342c850f8b9d69f304b53db46